While the present invention has application to a wide range of mechanical and electro-mechanical devices for the purpose of simplicity and clarity the invention will be discussed particularly as it applies to pumps. It is not intended to limit this invention to pumps or any other particular class of mechanisms.
In drilling a well for oil or gas, it is normal to employ piston type pumps (commonly referred to as "mud pumps") to circulate drilling fluid through the drill stem. The circulating drilling fluid serves a multitude of purposes including cooling and lubricating the drill bit and stem, removing drill cuttings and transporting them to the surface, preventing ingress into the hole of unwanted material such as oil, water, and gas, and owing to the weight and head of the column of fluid, in equalizing downhole pressure, thus minimizing the possibility of a well blowout.
Owing to importance of the circulating drilling fluid in the efficiency and safety of drilling for oil and gas, it is obvious that the mud pump which provides the circulation is equally important.
The mud pumps generally in use at the present are direct acting piston type pumps. These pumps fall into two general categories, i.e. two cylinder-double acting pumps typically referred to as duplex pumps and three cylinder single acting pumps, commonly referred to as triplex pumps.
Although different in some respects, both types of oilwell mud pumps have comparable maintenance problems. The components in the pump's fluid end, that is to say, the pistons, cylinder liners, valves, and valve seats (also rods and rod packing in duplex pumps) require renewal at rather frequent intervals, because of the abrasive nature of the liquid medium being handled. It is most important that the operator of the equipment be able to predict with reasonable accuracy the time at which these fluid end parts are likely to fail. In this way he may schedule pump maintenance during some safe, convenient period in the drilling program, for example while performing an operation for which the pump is not required. Without a suitable wear detecting device, the operator is likely to exchange expensive fluid end parts far too often, with attendant losses in drilling time and revenues, or run the risk that the pump will fail at some time crucial to the operation or safety of the well drilling operation.
It has been customary for some years in the industry to apply hourmeter clocks to the mud pumps, and thus record the quantity of hours which a particular pump has operated. It is well known, however, that inasmuch as the mud pumps operate over a wide range of speeds and pressures, the prediction of parts failures based on running time in clock hours is highly unreliable. In order to accurately predict failure of the fluid end parts of these pumps it is desirable to measure the work which has been expended through the part. The work, which is proportional to wear, which is expended by the pump is typically the product of three variables; namely speed, pressure, and time. Other variables, such as temperature, for example, may also be considered, depending upon the character of mechanical or electromechanical device under consideration. The present invention effectively provides means for measuring and recording the products of the variable wear inducing factors to which the pump or other apparatus is subjected during operation and thus provides the operator of the equipment with reliable signals representing the expected wear of the equipment that has occurred. Maintenance can be accurately and efficiently scheduled to insure optimum utilization of the equipment and to insure minimum repair induced down time of related equipment.